To fit in.

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1847.  I have no notion of spoiling sense to make it fay in with book rules; but I make the grammar come down to the sense, not the sense give up to the grammar.—D. P. Thompson, ‘Locke Amsden,’ p. 138 (Boston).

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1866.  

        Nothin’ but tells us wut we miss,
  Ther’ ’s gaps our lives can’t never fay in,
An’ thet world seems so fur from this
  Lef’ for us loafers to grow gray in!
Lowell, ‘Biglow Papers,’ 2nd S., No. 10. (N.E.D.)    

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1868.  It was one of the things that fayed right in.—Mrs. Whitney, ‘Patience Strong’s Outings,’ p. 128. (N.E.D.)

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1906.  The explanation of the canals as threads of vegetation fays in with the one which has been found to meet the requirements of the blue-green areas.—Percival Lowell, ‘Mars and its Canals,’ p. 347.

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